1. Field of the Invention
This invention relates to compounds formed by linking molecules containing carboxylic acid functional groups to phosphazenes via condensation to side-group amino residues.
2. Description of the Prior Art
There has been considerable interest in the use of polyphosphazene polymers as carriers of bioactive molecules since the discovery that polyorganophosphazenes having amino acid side-groups decomposed hydrolytically to produce harmless products consisting of amino acids, phosphate, and urea. Polyorganophosphazenes also offer a wide choice of side-group structures that can impart water solubility hydrophilic or hydrophobic insolubility, or in special cases, biodegradability, to non-toxic molecules. Since many bioactive molecules contain carboxylic acid functional groups, the linkage of carboxylic acids to phosphazenes via condensation to side-groups amino residues is an appealing prospect.
Many aminophosphazenes, such as [NP(NH.sub.2).sub.2 ].sub.x, [NP(NH.sub.2)(NHR)].sub.x, and [NP(NHR).sub.2 ].sub.x, are known, both as cyclic trimers or tetramers and as high polymers, as is disclosed in Allcock, Phosphorus-Nitrigen Compounds, Academic Press, New York, 1972. p-Aminophenoxyphosphazenes have also been synthesized, as disclosed in Kober et al, Inorg. Chem., 6, 394 (1967). However, all attempts to bring about coupling between aminophosphazenes such as these and carboxylic acids proved to be unsuccessful. Therefore, there still remains a need for a method of coupling carboxylic acids to phosphazene polymers.